Pneumatic control systems for electropneumatic transducers and other pneumatically operated devices are widely used in industrial processes and automated plants. Pneumatically operated HVAC control systems, due to the nature of building construction in which they are incorporated, present special installation and servicing problems. Typically, these control systems are not installed until construction is at least well under way, or completed. The control panels are usually installed first. Next, wiring is strung, pneumatic actuators are installed on the valves and dampers, and the pneumatic lines are "tubed." Finally, electronic controls for the HVAC system are installed.
During the construction and installation stages, which can be prolonged, some temporary means of HVAC operation is needed. Until the permanent system is fully installed, it cannot be used to position the pneumatically actuated valves and dampers. Also, the repair or replacement of a finally installed transducer or control device unavoidably disrupts the pneumatic supply.
Presently, construction workers and HVAC system installers and servicemen deal with these problems by "jerry-rigging" pneumatic control devices, a practice which can be time consuming, expensive and unreliable. Even after complete installation of the system, a sensing or other electronic problem can render the system inoperative. Repair of the electronic control system may even require disassembly of the pneumatic system.